Almost four years ago, Boko Haram kidnapped 276 schoolgirls from Chibok, in Borno State.
The aid workers are not believed to have been specifically targeted but were caught up in an attack on the military.
The fighters involved in Thursday's attack were armed with "automatic weapons, rocket propelled grenades and gun trucks", according to an official statement by the International Organisation for Migration (IOM).
"Boko Haram insurgents had launched a surprise attacked on us this Thursday night at Kaya which is very closed to military base, they looted food stuff, carted away with one vehicle and abducted three people", he said.
"Two of those killed were IOM field colleagues, " Mohammed Abdiker, IOM Director of Operations and Emergencies said.
Boko Haram held a swathe of territory in northeast Nigeria around the size of Belgium in late 2014.
But in the fresh video, Wakil said, "They are even the ones that called me and said Mama, we heard what you have said and told me that they are with the girls and they are going to release them".
"I begged of them and said 'please, let this not be another 1,000-plus days of Chibok girls, and they laughed and said no".
UNICEF, in a statement by Marie-Pierre Poirier, UNICEF Regional Director for West and Central Africa, also expressed shock on the attack against humanitarian workers in Rann.
"Prior to the attack, the roughly 40,000 people living in Rann were relying nearly entirely on MSF's services to access health care", the group (also known by its French name, Médecins Sans Frontières, or MSF) said in a statement.
"One of these courageous workers who lost their lives, and the nurse who is missing, were on the frontline providing critical services supported by UNICEF". All those involved were Nigerian, she added. "We will continue to evaluate how the situation evolves and we will return as soon as the conditions allow".
The United Nations for the Office of the Coordination of Humanitarian Affairs in a statement on Friday by its spokesperson, Samantha Newport, confirmed the death of its three workers, noting that three other workers were injured by the insurgents. A local nurse was also injured. Those responsible for these and other atrocities in Nigeria must be apprehended and prosecuted.